[SSSD] [sssd PR#486][opened] TOOLS: Fix typo: exist -> exists

[fidencio]

   URL: https://github.com/SSSD/sssd/pull/486
Author: fidencio
 Title: #486: TOOLS: Fix typo: exist -> exists
Action: opened

PR body:
"""
I've noticed the typo while working on #472 
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/486/head:pr486
git checkout pr486